Hey everyone, Thought I might start a thread on a little project I'm doing to try to learn about some of the pitfalls of preamp construction. When finished, I hope it will give me a place to try some different stuff. The PS is on a seperate chassis and consists of a CT TX, 6CA4, 10hy choke/25uf motor run cap, 5hychoke/motor run. It's putting out 211v into a 90ma test load. The filament supply is an old CDP PS which after a couple resistor changes is putting out ~ 25v of heavily filtered DC. I plan on running the 12B4 filaments in series, at least for now. The amplifier section will be a 12B4 per channel, with a 5k plate resistor. I'm thinking 100ohm resistor and 1000uf cap on the cathode? I have an assortment of output caps to try ranging from 3uf on up. Anyone ever use tantalium caps or motor run oilers for coupling? Anyhow, I hope to be able to design something someday, but for now I just have a lot of fun "slingin solder". If this gets to sounding like something I want to build for keeps, an RIAA stage will be the next project. Any comments, suggestions, or general poking fun is allways welcome and thanks in advance, Jay

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"Make everything as simple as possible, but no simpler" Einstein

Very good reading there Geek, thanks for the link. I checked out your sites as well............very cool. Most of the new motor runs that I'm finding on the cheap at AC supply houses (2 or 3 bux) are made in China. I think I'll cut one open and see what they are made of. Jay

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"Make everything as simple as possible, but no simpler" Einstein

Just thought I'd post a follow up. I finished this thing today, and am quite impressed with the 12B4A. I used some Japanese IECs which are apparently a good variety (I've heard you have to find good 12B4s). The sound is very good from top to bottom after a couple hours "burn in". I ended up with 220v B+, which gave me ~60v on the plates via a 4.7K resistor. I had a bit of trouble on one channel at first (High pitched squeal) but after changing the grid stoppers to 500 ohm, and replacing a suspect interconnect, all is well. I've allways been an octal fan, but this little 9pin has made a beleiver out of me. It has plenty of gain to make my 2A3s happy. I think I will build it for real, and add a RIAA circuit. I've never done an RIAA before, does anyone have a favorite? Oh yeh, I ended up using a .50uf output cap, and 1000uf cap with 100ohm R on the cathode. Jay

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"Make everything as simple as possible, but no simpler" Einstein